F. Todd Baker

A test of the DWIA at 135 MeV using the 207Pb(p, p′) reaction

Abstract Data for the excitation of the strongly collective octupole doublet in 207Pb at EX = 2.64 MeV is used to test the distorted wave impulse approximation (DWIA) at a proton bombarding energy of 135 MeV. A complex, effective local interaction derived from the nucleon-nucleon phase shifts is used together with the wave functions of Ring and Speth for the low-lying octupole state in 208Pb. The DWIA (including central and spin-orbit terms) is found to be in reasonable agreement with both the magnitude and shape of the observed cross section.

The 90,92Zrd(p,p′) reactions at Ep = 800 MeV+

Abstract Angular distributions of analyzing powers and differential cross sections have been measured for elastic and inelastic scattering of 800 MeV protons from 90 Zr and 92 Zr. The data have been interpreted using both the collective-model distorted-wave Born approximation and the semimicroscopic distorted-wave impulse approximation with the Love and Franey t -matrix. Clear differences in the data for transitions to both the 2 + 1 and the 4 + states in the two nuclei, attributable to differences in the microscopic structures of the states, have been observed. These differences are only partially explained by the semimicroscopic analyses. Interpreting the A y data with the help of recent data-to-data relations suggests that the free L · S interaction used at 800 MeV is incorrect.

194,198Pt(p, ṕ) reaction and the interacting boson model

Abstract Angular distributions of d σ/ d Ω and Ay were measured for low-lying collective states, Jπ = 01+, 2+1, 2+2, 4+1, 4+2, 4+3 in 194,198pt using 135 MeV polarized protons. Coupled-channels analysis of the data indicates large E4 moments for the 4i (i = 1, 2, 3) states in both the isotopes. These data have been analyzed in the framework of the interacting boson model (IBM). Although the standard IBM-1 scheme with only s- and d-bosons can describe the E2 properties of both isotopes quite well, a more generalized version which also includes a g-boson is needed to correctly reproduce simultaneously both the E2 and E4 data. Another model using the “projected IBM-2” parameters gives similar results.

A new rigid asymmetric-rotor model description of the heavy transitional nuclei

Abstract Hexadecapole shape components have been added to the usual Davydov-Filippov asymmetricrotor model and this extended model has been applied to the nuclei 184, 186 W, 186, 188, 190, 192 Os, 192, 194, 196 Pt, and 198, 200 Hg. This model provides a much improved description of the E2 properties and in addition predicts correctly the known E4 properties. E2 properties previously thought to be anomalous (phases and magnitudes of matrix elements involving the second 2 + states) are correctly predicted.

192Os(α, α′) reaction at Eα = 24 MeV and the IBA model

Abstract Angular distributions of 24 MeV alpha particles elastically and inelastically scattered from 192 Os have been measured for the angular range θ lab = 50°–140°. Data are reportedhere for 0 + , 2 + 1 , 2 + 2 , 4 + 1 , 4 + 2 and 4 + 3 states. Coupled-channels analysis of the data was performed using matrix elements predicted by the interacting boson model assuming 192 Os to be a perturbed O(6) nucleus. Fits to the data are excellent for the ground band (0 + , 2 + 1 , 4 + 1 ), fairly good for the quasi-gamma band (2 + 2 , 4 + 2 ), and poor for the K = 4 band (4 + 3 ).

192Os(p, p') reaction at 135 MeV

Abstract Angular distributions of dσ/dΩ and A y for excitation of 0 1 + , 2 1 + , 2 2 + , 4 1 + , 4 2 + and 4 3 + states in 192 Os by 134.5 MeV protons have been measured. Results for quadrupole transitions are in good agreement with previous results. For the L = 4 transitions to the first three 4 + states, quite large strengths are observed, much larger than expected from IBM1 calculations, particularly for the 4 3 + state.

A comparison of t-matrix and G-matrix analyses for the 207Pb(p, p') reaction at Ep = 95 MeV

Abstract Angular distributions of differential cross sections for elastic and inelastic scattering of 95 MeV protons from 207 Pb have been measured over the angular range of 8–70°. The data have been analyzed using collective-model and semimicroscopic-model distorted-wave calculations. Semimicroscopic-model calculations were done with both G -matrix and t -matrix interactions; spectroscopic results and fit qualities were found to be essentially the same for these two interactions. When compared with earlier work at 61 and 135 MeV the present results are generally in good agreement with or fit into reasonable trends with these results at other energies. However, rather serious discrepancies with electron scattering results exist.

Heavy-ion excitation of 3− states in deformed nuclei

Abstract Previously measured data for 70.4 MeV 12 C excitation of 3 − states in 148, 150 Nd are reanalyzed using a third-order rotational-vibrational model. Calculations using 3 − quadrupole moments which are expected if they are K = 0 states are in reasonable agreement with the magnitude of the large-angle data, but the quality of the fit in the Coulomb-nuclear interference region is only fair. It is found that the matrix element 〈2 + ∥ M (E3)∥3 − 〉 plays an important role in the calculations making the “measurement” of the 3 − quadrupole moments very difficult, if not impossible.

Nuclear reorientation effects for the 26Mg, 28Si(12C, 12C′) reactions at E = 41 MeV

Abstract Angular distributions for elastic and inelastic scattering of 41 MeV 12 C from 26 Mg and 28 Si have been measured. Corresponding angular distributions from coupled-channels calculations show significant differences depending on whether a prolate or an oblate intrinsic shape is assumed. The 26 Mg and 28 Si data are best described by calculations with prolate and oblate shapes, respectively, in agreement with previous Coulomb excitation rorientation measurements. The Hendrie scaling procedure fails to accurately predict the measured nuclear β 2 deformation for 26 Mg.

Sensitivity of (α, α′) cross sections to excited-state quadrupole moments

Abstract Angular distributions for excitation of the 1.20 MeV second 2+ state in 180Hf by 21 and 24 MeV α-particles have been measured. Coupled-channels calculations show substantial sensitivity to the assumed quadrupole moment of this state. The data are best-fitted by calculations using the value of the quadrupole moment expected if the state is a simple λ-vibrational level.